1. Field of the Invention
Alternative and synthetic fuels such as fatty acid methyl ester (FAME), vegetable oil, liquefied biomass (biomass-to-liquid [BTL]), liquefied gases (gas-to-liquid [GTL]), etc. are becoming increasingly important. However, with respect to their material properties such as density, viscosity, heat value and combustion value, thermal capacity, aromatics content, oxygen content, hydrogen content, carbon content, inorganic impurities (alkaline metals, alkaline earth metals), phosphorus content, sulfur content, storage life, boiling temperature, and sonic velocity, etc., they differ from the standardized, authorized fuels that are used for engine design and engine acceptance and which are required by law.
In order to detect this difference in fuel and respond to it if necessary, it would be useful to determine the fuel characteristics during operation.
2. Description of the Related Art
The emissions, exhaust gas temperatures, maximum engine output, and peak cylinder pressures change when internal combustion engines are operated with these nonstandard fuels.
The altered exhaust gas emissions may exceed legally prescribed limits. NOx emissions, for example, are increased when using FAME, while particulate emissions decrease.
When catalytic converters are used, altered gas emissions may come about as a result of a decrease in the exhaust gas temperatures due to a deviating combustion value or delayed ignition that the light-off temperatures can no longer, or rarely, be achieved, which results in worsened emissions. On the other hand, an increase in exhaust gas temperatures can cause thermal damage to the catalytic converters.
At the same time, the use of biofuels lead to an accelerated chemical deactivation of the catalysts for aftertreatment of exhaust gas due to the increased amounts of alkaline metals and alkaline earth metals, phosphorous, and sulfur.
Since the fuel system and engine oil circuit are usually not hermetically isolated from one another, a mixing of fuel and engine oil results. Therefore, the use of unauthorized fuel leads to an uncontrollable change in the material properties of the engine oil, which can lead in turn to engine damage.
DE10346314A1 describes a generic sensor that can be used to determine the viscosity of fuel. For this purpose, the fuel is made to oscillate by an actuator and these oscillations are detected by a pressure sensor. The viscosity can be determined by evaluating the pressure curve. The disadvantage of this method consists in the need for an actuator which increases costs and makes maintenance more cumbersome.
DE10152236A1, DE10217376A1 and DE10217379A1 describe methods by which the fuel characteristics are determined from the vapor pressure of the fuel. For this purpose, the vapor pressure in the fuel tank and/or fuel system is determined. During this process, it is absolutely necessary that the engine does not take any fuel from the fuel system, i.e., the engine must be turned off. Therefore, this method cannot be used in engines which cannot be turned off such as engines for power units, combined heat and power plants, compressors, etc. Further, in order to determine the vapor pressure it is necessary to isolate the volume in which the pressure measurement is carried out from the environment or even to generate a slight vacuum pressure in this volume. This makes it necessary to use shutoff valves and/or vacuum pumps which results in high costs and correspondingly high maintenance expenses.
DE10015162A1 describes a method in which the combustion noise is detected and the quality of injection, i.e., the start of injection or rate of injection, is determined from this combustion noise. The drawback in this method consists in that the combustion noise cannot be used to determine the fuel being used because it is also influenced by a number of other factors such as tolerances, the degree of fouling or wear of the injection nozzle, injection pump, inlet valves, outlet valves, exhaust gas turbocharger, etc. Since the combustion noise largely depends upon the energy that is released, this method can only be used to determine the volumetric heat value, the start of injection or the injection rate with sufficient accuracy because of the customary volumetric addition of fuel to the combustion chamber. Since it is not possible to determine viscosity or compressibility, no definite conclusions may be drawn about what fuel is being used. Rather, this method is mainly used for improving smoothness of operation.
In DE19955796B4, fuels are distinguished by an angularly resolved measurement of the acceleration of the crankshaft and, therefore, of the energy released. Similar to Patent DE 10015162A1, this method only allows the volumetric heat value to be determined with sufficient accuracy, but determination of viscosity or compressibility is impossible. No definite conclusions can be reached about the fuel that is used. Rather, this method is again chiefly used to improve smoothness of operation.
DE4019083A1 describes a method in which the fuel quality is determined by a lambda sensor or fuel quality sensor, and the engine parameters are modified in accordance with this information. The disadvantage of these sensors consists in that they are very sensitive and expensive.
Further, the sensors are usually used to improve the smoothness of operation of the engine and/or the starting behavior. Adaptation of emissions is not described, nor is the effect of unauthorized fuel on engine oil characteristics.